The United States on Thursday joined more than 20 countries in creating 40 new marine sanctuaries around the world to protect oceans from the threat of climate change and pollution.

The sanctuaries, unveiled at a high-level conference in Washington, limit commercial fishing, oil and gas drilling, and other human activity that affects ocean ecosystems.

Altogether, countries at the oceans conference will announce new sanctuaries covering nearly 460,000 square miles (1.19 million sq km) of ocean, an area around the size of South Africa.

President Barack Obama designated the first U.S. marine reserve in the Atlantic Ocean: 4,913 square miles (12,724 sq km) known for their underwater mountains and canyons off the coast of New England.

Obama, who recalled body-surfing in the Pacific Ocean while he was growing up in Hawaii, called the pledges a “pretty good down payment” but said bolder international action was needed.

“The notion that the ocean I grew up with is not something that I can pass on to my kids and my grandkids is unacceptable, it’s unimaginable,” Obama told the conference.

Last month, Obama expanded a massive reserve off the coast of Hawaii – the world’s largest such protected area – as he works to cement his environmental legacy before his time in the White House ends in January.

He traveled to the remote Midway Atoll in the reserve, and told the conference what it was like to snorkel among purple and orange coral as endangered monk seals sunned themselves on nearby rocks.

“I saw it. It was right there, evidence of the incredible power of nature to rebuild itself, if we’re not consistently trying to tear it down,” Obama said.

Opponents of the new Atlantic reserve have complained that it threatens the commercial seafood industry in the region. But Obama said it was designed to respect the fishing industry’s role in the region’s economy and history.

The conference will emphasize the urgent need to combat illegal fishing, pollution from plastic debris, and the acidification of the ocean, which is destroying coral reefs and shellfish, said Catherine Novelli, the U.S. undersecretary for economic growth, energy, and the environment at the State Department.

“We’re expecting over a hundred new initiatives that are going to be worth billions of dollars,” Novelli told reporters.